The project will be directed toward a genetic and biochemical analysis of the branched chain amino acids in Escherichia coli. The effects of gene mutation and physiological manipulation on the normal, multivalent repression pattern of control over the levels of 4 of the 5 enzymes required for isoleucine and valine biosynthesis will be examined in terms of enzyme activity and enzyme amount and in terms of mRNA levels and stability. The analysis will attempt to identify the various elements involved in this multivalent control. A similar attack will be made on the mechanism of induction of the fifth enzyme required for isoleucine and valine biosynthesis. The transcription and translation in vitro directed by ilv DNA will be studied to account biochemically for the roles of the regulatory elements discovered during in vivo experiments.